The Stovebolt Site Forums The Shop Area Engine Shop Thermostat question

I have a 250 6 cylinder engine in my '59 3100. When I start it when it is cold, the engine has to warm up quite a bit more than the rating of the thermostat before the water temperature gets hot enough to open the thermostat. The temperature sending unit is right above the thermostat so you can see the temperature spike of about 30 degrees when the thermostat opens and the hot water reaches the sending unit. It then goes way down when the cold water from the radiator cycles though. After the first cycle of the thermostat opening and closing, the temperature spike is not nearly as drastic. I was thinking of drilling a small hole in the thermostat so that there would always be a small amount of coolant circulating all the time. It seems like this would even out the engine temperature. What do y'all think?
Thanks a lot,
Gene

A lots of us do that very thing. Nothing wrong with doing it.🛠

I was thinking that I had heard that they made some thermostats that already had a hole in them but I haven't ever seen one and I figured that I should ask someone else before I went to modifying one. I was thinking about a 1/8" hole. I wouldn't think it would take much.

Yes you can buy them already drilled. NAPA should have them.🛠

Gene, thermostats manufactured with holes drilled through them typically also have what it is called a jiggle pin. The jiggle pin looks like a loose rivet that sticks through the hole with the rivet head on the engine block side of the thermostat. It that functions like a check valve by allowing trapped air to escape from the block but not to allowing coolant to pass through. This would defeat what you are trying to do. If you Google search 'jiggle pin', you'll see examples.

Matt

You can loop the heater hose to return back to the water, the water will circulate better. I moved my sending unit to the thermostat housing just below to the thermostat. This made my gauge look a lot better and I quit working about the spike in temperature.

Thanks for all the replies. I checked out NAPA and found one with a jiggle pin. It looks like it would be easy to remove the pin but the thermostat is $24.95. I think that I paid about $6.00 for my last one and it would be just as easy to drill a hole as it would be to get the pin out. I figured that looping the heater hose would help because the problem isn't as bad with the heater on but it still spikes somewhat. I think I will just go back to my original idea and drill a hole in the thermostat. I appreciate all the information.
Thanks again,
Gene

Drill a small hole.

My engine ( 1970 250 ) had the sender in the head, between #1 and #2 cylinders. I would always see 25 degrees or more over thermostat setting before the engine began to cool off to the actual thermostat degree ( 180 ), I worried every time I set out on a trip. Once I moved the sender, the spikes went way down. I have since added an aluminum radiator and rerouted my hoses, so I gained about a gallon more coolant then the stock setup had. This also helped level the temperature.

A 3/32" hole should do fine. If you find it still worries you, try moving the sender to the hot side of the thermostat, or just don't look at it till you get down the road a mile or two!

There are reasons for a lag time in the system. The real question is what are the actual temperatures during warm up, 30 deg spike....and final running temp. It would be nice, before you drill the hole, to test the thermostat on your stove with a good thermometer. This is a must do on a $6 Chinese thermostat. Which before box price, shipping, taxes, mark up and taxes again was 23 cents to make including material and labor.
The initial water pressure fights against the first opening of some thermostats. If the temps are indeed within safe range during this period, it's no problem.

The stove test will not replicate the opposing pressure but will indicate the static lag time and the calibration of the stat. The stat should break the seal at no more than 4 deg from rating. It will be fully open at 15-20 ABOVE rated.
Source: Stant

Drilling a hole is a band aid and may cause heat problems. There are a lot of things that do work OK. They were discovered by folks who lived far from town, low on cash and time. I'm not against what works. Lots of innovations were discovered that way. Lot's of folks took out the stat also, that's not good, but is still advised now and then.

Just tried to test my old and new Tstat in the kitchen, couldn't get the water hot enough to open a 195F Tstat.

Ed

Ed, your water boils at 203 Deg., so if the water boiled and it didn't even crack, you are a tad over spec. Drive to the ocean and try it.

Bartamos, I am using a stant thermostat and I did test it on the stove. Everything is working fine, it just seems like a design flaw to me that the hot water doesn't get to the thermostat earlier. Thanks for the advice though.

I used to call him bart until I heard the story behind the handle. Then I felt horrible about leaving Amos out of the picture all those times.
bartamos definitely needs to delete his off topic post. We don't want to confuse folks about him having feelings and a soul.
(He does have both, BTW)
Carl

Sorry Bartamos, I still didn't realize that I mispelled your name. I am kind of slow some times.

Thanks Gene. You are not the first. I try to keep track of names myself.
Thanks for the words 53Karl.